A broadband communications system includes data sources, a broadcasting network, a headend unit, and edge devices. The data sources can be encoders and video sources that send data through an uplink to the broadcasting network. In the broadcasting network, three common types of signals received at the headend include off-air signals, satellite signals, and local origination signals. The satellite signals include any signal transmitted from an earth station to an orbiting satellite which are then retransmitted back down to earth. The signals are transmitted from earth to the orbiting satellite on a path referred to as the uplink. These signals are then received by a transponder on the satellite and are retransmitted from the transponder to a receiving earth station over a downlink. The transponder amplifies the incoming signal and changes its frequency for the downlink journey to avoid interference with uplink signals.
The headend (HE) or central office is where signals from multiple sources are received and are conditioned and prepared for transmission over an access network to subscribers. Once signals have been prepared for delivery, they are combined onto a medium to be sent over the access network to the customer premise devices. Conditioning may include conversion of analog to digital, digital bit-rate conversion, conversion from variable bit rate to constant or clamped bit rate, conversion of multiple-program transport streams to single-program transport streams or any other type of grooming or combination of these. The medium may include coaxial, twisted pair or other cable, optical fiber, or some form of wireless transmission. The preparation for transmission in edge devices may include generation of an RF carrier, modulation, conversion to optical, frequency division multiplexing, time division multiplexing, wavelength division multiplexing or any combination of these. Edge devices vary depending on the type of network, and include the headend output devices. These edge devices sometime overlap with or extend into an access network. The fiber access network can include an optical line terminal (OLT), an optical node terminal (ONT), and devices inside the home. Therefore, the OLT and ONT may be considered either an edge device or an access network device. However, the ONT may at times be considered a customer premises device. A hybrid fiber/coax (HFC) network typically uses modulator edge devices. An HFC access network can include RF to optical converters, optical to RF converters, optical and RF amplifiers, optical and RF combiners, splitters and taps. HFC customer premises devices include RF modems and set-top boxes. A digital subscriber line (DSL) network can include a digital subscriber line access multiplexer (DSLAM). DSL modems are usually located in customer premises. The OLTs, modulators, and DSLAMs, also known as edge devices, service numerous user homes, such as a neighborhood in a city. Customer premise devices can include modems, routers, personal computers, set-top boxes (STB), etc.
FIG. 1 illustrates a satellite broadcast network 100. At an uplink facility 110, program content is stored on video servers controlled by a broadcast automation system. Any analog content at a network operations center (NOC) 120 is compressed using encoders and then multiplexed with the content delivered from the video file servers. The NOC 120 is responsible for overall control and co-ordination of the uplink and the downlink sites. A headend (HE) 130 may include one or more server devices for providing broadband signals such as video, audio, and/or data signals. The headend 130 also has numerous decoders which preferably each have a mass storage device, such as a hard disk drive.
Broadband communications systems, such as satellite and cable television systems and DSL, are now capable of providing many services in addition to analog broadcast video, such as Video-on-Demand (VOD), personal video recording (PVR), HDTV, Interactive TV, Web TV, online gaming, telelearning, video conferencing, voice services, and high speed data services. With an increase in the number of services offered, the demand for bandwidth has drastically increased. A switched digital video (SDV) system is a technique that delivers selected services only to homes where and when users are actively requesting service. The switched digital video technique would be performed in the SDV devices, which vary depending on the type of network. A common problem using the SDV technique occurs when devices in a user's home requesting services requiring more aggregate bandwidth than can be provided. The SDV devices can not currently track the bandwidth being requested, so an attempt is made to honor all requests. This results in oversubscribing and a loss of packets.